The present invention relates to a method and a circuit for controlling the air-fuel ratio of an internal combustion engine in which the output voltage of an oxygen measurement probe which is arranged in the exhaust gas duct of an internal combustion engine is fed to a controller, and the controller gives off a correcting variable for the air-fuel ratio.
By controlling of the air-fuel ratio in this type of engine, it is desired primarily to reduce the quantity of noxious substances in the exhaust gases emitted by the internal combustion engines. There is known for this, for example, a method in which an oxygen measurement probe is arranged in the stream of the exhaust gas of the internal combustion engine, the probe contolling an integrating device, and the output signal of the exhaust gas measurement probe being connected to a threshold switch, and switching the latter upon the occurrence of the threshold value, the direction of integration of the integrating device being changed upon the switching of the threshold switch. As a function of at least one operating parameter of the internal combustion engine, in particular as a function of the amount of intake air of the internal combustion engine, the time constant of the integrating device is changed. The integrating device of variable time constant proposed in connection with the known method does not however satisfy the requirements with respect to accurate and adaptable regulation.
Accordingly it is an object of the invention to provide a method and a circuit therefor not having the above-mentioned disadvantages.